1. Field of the Invention
The present invention relates to supersonic and subsonic lasers which have a gaseous active medium, a nozzle, a RF discharge region, a laser active region, and an optical resonator.
2. Discussion of the Prior Art
Known gas laser systems use electrical discharges between DC or AC electrodes within transfer or axial flows. However, utilization of DC or AC electrodes, within fast subsonic and especially supersonic flows, creates unstable and non-uniform (in time and space) plasma discharges. These non-uniform discharges produce aerodynamic instability of the gas flow. This instability, characterized by wave shocks and turbulence, is proportional to the static pressure of the flow and volume of the discharge region between DC or AC electrodes. These limitations prevent creation of a stable, uniform and continuous plasma. AC/DC electrode discharges also create an additional aerodynamic resistance for gas flows which results in the necessity of a much higher power gas pump.
The aerodynamic instability of the supersonic and subsonic flows generated in the known gas lasers also produce regions of increased temperature, related to the wave shocks, as well as temperature pulsations, related to the turbulence. These factors are responsible for reduction of the laser inversion population, efficiency of the laser and optical quality of the flow within the resonator region.
Gas medium excitations, utilizing glow DC or AC discharges, are also well known. These laser designs, however, have other fundamental problems.
Glow discharge lasers are known to cause a low level of excitation density energy into discharge per one volume unit of plasma above which sparking takes place (i.e. are plasma areas). Thus, prior art designs may cause the creation of these localized arc plasma with a relatively short life time which will occur if the current density is higher than a critical level when glow plasma loses stability.
The arc plasma regions create a high atomic temperature of the laser gas which, like the result, will be free from laser activity. Thus, to maintain proper population inversion, these arc plasma areas must be kept to a minimum, something which is difficult to do utilizing prior art glow discharge type lasers.
Relative to the RF glow discharges, DC or AC glow discharges have a much less possible energy contribution to the same volume of stable non-equilibrium plasma. Typically, RF density requirement for excitation has ranged from 10 to 100 watt per cubic centimeter, depending on RF frequency and type of RF plasma (Alpha or Gamma). In the case of DC and AC glow discharges for identical gas conditions, the range of maximum possible density is only from 1 to 5 watt per cubic centimeter above which the sparking-plasma instability takes place.
There is additionally a principle difference between the nature of RF and DC/AC plasma structures. DC or AC discharges are based on the direct current of electrons and ions between an anode and a cathode. RF or a High Frequency Discharge structure is based on the high frequency oscillation of electron""s boundaries located on the RF electrodes and stimulation of a xe2x80x9cPositive Columnxe2x80x9d of ions and negative electrons between RF electrodes with the help of high frequency ionization by collision actions. This means that DC and AC discharges are much more capable of the disintegration of chemical stability of the laser gas medium, based on the dissociation, for example of CO2 molecules to molecules of CO and atoms of O. That is why RF discharges are preferable to DC/AC type of discharges in the areas of chemical stability of the laser gas, energy contribution to the volume of the plasma, optical quality of the active medium and the power requirements for the gas pump for providing gas flow.
The present invention is for a supersonic or subsonic laser having radio frequency (RF) excitation and utilizing a gaseous flow of active medium. The laser of the present invention uses radio frequency (RF) excitation to generate a non-equilibrium plasma in the area of the sonic/subsonic or supersonic/subsonic gas flow. The high frequency excitation may occur within the critical area of the supersonic nozzle or downstream from the critical area within the nozzle. The laser of the present invention uses radio frequency RF excitation to generate a non-equilibrium plasma in the area of the sonic/subsonic or supersonic/subsonic gas flow. The high frequency excitation may occur within the critical area of the supersonic nozzle or downstream from the critical area within the nozzle.
The laser consists of a gas supply line which provides the gaseous medium into a receiver area. The gas may be supplied into the laser at a predefined pressure, depending upon the specific type of gas utilized. The gas passes through the supply line at slow subsonic speeds.
A supersonic nozzle opens into an optical resonator region and also contains a localized excitation area. The laser of the present invention may have a two-dimensional or flat nozzle interior.
The laser device of the present invention provides for high output power of laser generation and highly efficient use of the gaseous active medium in order to generate an extremely efficient laser while utilizing a simplistic design and relatively low energy supply. The laser can use various gases or mixtures of gases in combination with radio frequency discharge excitation between a large rectangular flat RF electrode and an opposite grounded laser body in the area of sonic/subsonic or supersonic/subsonic flow of the gas active medium.
The laser of the present invention utilizes a radio frequency (RF) discharge which creates a non-equilibrium xe2x80x9cAlphaxe2x80x9d or xe2x80x9cGammaxe2x80x9d plasma through ionization and electron excitation of high states of atoms, molecules or ions in order to achieve a high inversion population necessary to generate lazing activity in the optical resonator region.
The laser of the present invention has a high frequency discharge region between the wide linear RF electrode and the grounded metal body of the tunnel or nozzle in the area of the sonic/subsonic (M=1/M less than 1) or supersonic/subsonic (M greater than 1/M less than 1) flow of the gaseous active medium. Radio frequency (RF) excitation action creates almost uniform distributions of ions PC (xe2x80x9cPositive Columnxe2x80x9d) and electrons into the discharge region. The radio frequency discharge region is located between the plane RF electrode and the grounded opposite side of the dielectrically insulated nozzle portion and can be located within the critical area of the supersonic nozzle or downstream of the critical area within the supersonic area of the nozzle.
The excitation region of the laser may have a more extensive area relative to the discharge region, depending upon the active medium or the pressure of the gas and may occur within the critical and supersonic areas of the nozzle up to the beginning of the optical resonator area. Alternatively, the location of RF electrode and discharge region can be partially coextensive or coextensive with the optical resonator region.
Within the optical resonator region is located the laser active region. This region is transferred by the resonator beam phases thereby taking advantage of the maximum level of laser inverse present and generating resonance photon amplification. The lasers generated by Radio Frequency excitation of the present invention may be within the wavelength range from 0.4 um. for Ar and up to 10.6 um. for other gases.
Located downstream and at the end of the receiver area is a supersonic nozzle. The two-dimensional supersonic nozzle has an optimal profile which may be symmetrical or asymmetrical to insure a quiet supersonic/subsonic flow having an uniform transverse distribution of thermodynamic parameters allowing for the adiabatic expansion of the gases within the nozzle. The supersonic nozzle opens into and within the optical resonator region to insure parallel supersonic/subsonic flow within the supersonic area of the nozzle. The supersonic area of the nozzle occurs down stream from the critical section of the nozzle. The laser head may be integrated with the RF resonator or with an RF amplifier as part of the power supply.
The present invention includes a radio frequency excited laser comprising a laser body retaining a gas medium within a gas flow path, said gas medium entering in a gas inlet and passing longitudinally through a nozzle, at least one RF electrode operably connected to an RF resonator, said RF resonator powered by an RF power supply, a dielectric plate insulating said at least one RF electrode, a dielectric coating opposite said gas flow path from said dielectric plate separating said laser body from said gas flow path, wherein said laser body adjacent said dielectric coating is grounded, an optical resonator within said gas flow path, at least one turbine in flow communication with said gas flow path, and an RF matching device operably connected to said at least one RF electrode and said RF power supply.